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The development of photoelectrochemical processes for pollutants elimination and hydrogen production via water splitting have attracted considerable attention in order to meet the global challenges of environmental pollution and energy demand. The efficiency of photoelectrochemical devices essentially relies on the semiconductor-based photoelectrode design with respect to solar light harvest and conversion. Among various architectures, highly-ordered and vertically-oriented TiO2 nanotube arrays (NTAs) and TiO2 nanowire arrays (NWAs) are extensively studied. However, the practical applications of TiO2 NTAs and TiO2 NWAs are significantly hindered by their wide band gap (3.0-3.2 eV) and fast charge recombination. Coupling TiO2 with semiconductors of narrower band gap can effectively expand light absorption range and improve carrier transport in the formed hybrid. Novel phosphorus-doped graphitic carbon nitride (P-C3N4) was first developed to modify TiO2 NTAs successfully by a facile polymerization in the present study. The prepared P-C3N4/TiO2 heterojunction exhibits enhanced light-absorption characteristics and improved charge transport ability, thus resulting in a 3-fold photocurrent (1.98 mA cm-2 at 1.0 V vs reversible hydrogen electrode (RHE)) increase from that of pristine TiO2 NTAs, giving a H2 evolution rate of 36.6 μmol cm-2 h-1 at 1.0 V vs RHE under solar light illumination. A structure composed of TiO2 nanowire arrays (NWAs) was further designed by decoration with graphene-linked graphitic carbon nitride (GCN) layers, serving as a robust photoanode for solar-driven water splitting. Under solar light, the optimal GCN/TiO2 NWAs photoelectrode produces a photocurrent density of 1.7 mA cm-2 at 1.23 V vs RHE, around 2.6 times higher than that of pristine TiO

In this study, we report a unique design of nano-porous bismuth vanadate (BiVO4) photoelectrode decorated with graphene linked carbon nitride (GCN) nanosheets and their potential application in solar driven photoelectrochemical water oxidation. Especially, an integrated sandwich-like heterojunction with highly interconnected porous structure, comprising two dimensional GCN sheets and three dimensional BiVO4 was successfully synthesized with significantly enhanced photoelectrochemical activity. The prepared photoelectrode achieves up to 1.98 mA cm−2 (1.23 V vs RHE) under AM 1.5G solar light irradiation, 2.06 times compared with pristine BiVO4 (0.96 mA cm−2 at 1.23 V vs RHE). After deposition of cobalt phosphate nanoparticles as water-oxidation electrocatalyst, a plateau photocurrent of 3.42 mA cm−2 (1.23 V vs RHE) with a maximum photo-conversion efficiency of 1.28% was achieved on the prepared photoanode. The highly improved photoelectrochemical performance can be attributed to suitable band matching facilitating efficient charge separation between GCN and BiVO4 as well as the desirable incorporation of rational designed dimensionality-dependent heterojunction for promoted solar energy utilization. More importantly, the combined experimental results and computational simulations reveal that the strong donor-acceptor coupling between GCN sheets and porous BiVO4 facilitates the separation and transfer of photoinduced electron-hole pairs, accounting for the highly promoted photoelectrochemical performance.

In this study, an efficient heterojunction was constructed by anchoring graphitic carbon nitride quantum dots onto TiO2 nanotube arrays through hydrothermal reaction strategy. The prepared graphitic carbon nitride quantum dots, which were prepared by solid-thermal reaction and sequential dialysis process, act as a sensitizer to enhance light absorption. Furthermore, it was demonstrated that the charge transfer and separation in the formed heterojunction were significantly improved compared with pristine TiO2. The prepared heterojunction was used as a photoanode, exhibiting much improved photoelectrochemical capability and excellent photo-stability under solar light illumination. The photoelectrocatalytic activities of prepared heterojunction were demonstrated by degradation of RhB and phenol in aqueous solution. The kinetic constants of RhB and phenol degradation using prepared photoelectrode are 2.4 times and 4.9 times higher than those of pristine TiO2, respectively. Moreover, hydroxyl radicals are demonstrated to be dominant active radicals during the pollutants degradation. © 2016 Elsevier B.V.

Graphene oxide/polydopamine-coated Si nanocomposite (GO/PDA-Si) was synthesized by a novel facile solution-based chemical method at room temperature. The nanocomposite with a PDA coating layer of similar to 1.5 nm exhibits a high reversible specific capacity and excellent cycling stability (1074 mAh g1 after 300 cycles at 2100 mA g(-1)) as an anode material for lithium ion batteries. The synergistic effect of the PDA coating layer and GO plays an important role in improving the electrochemical lithium storage performances. Both of them can serve as a cushion to buffer the volume change of Si nanoparticles (NPs) during the charge/discharge process and prevent Si NPs from direct contact with a liquid electrolyte. The surface property of Si NPs was also modified by introducing secondary amine groups, which can form amide groups with carboxyl groups and hydrogen bonds with hydroxyl/carboxyl groups on GO. These chemical interactions firmly anchor Si NPs to GO so that aggregation of Si NPs can be mostly prevented. Moreover, the good lithium ion conductivity of PDA is beneficial for rate performance. The experimental results should be very useful in guiding the preparation of long-cycle-life Si-based anode materials with good rate performance using a simple surface-modification process.

Novel phosphorus-doped graphitic-carbon nitride (P-C3N4) modified vertically aligned TiO2 nanotube arrays (NTs) were designed and synthesized. They can significantly enhance the conduction and utilization of photogenerated charge carriers of TiO2 NTs. The heterostructure was successfully fabricated through a three-step process: electrochemical anodization and wet-dipping followed by thermal polymerization. The prepared P-C3N4/TiO2 NTs exhibit enhanced light-absorption characteristics and improved charge separation and transfer ability, thus resulting in a 3-fold photocurrent (1.98 mA cm(-2) at 0 V vs. Ag/AgCl) compared with that of pure TiO2 NTs (0.66 mA cm(-2) at 0 V vs. Ag/AgCl) in 1 M NaOH solution. The prepared P-C3N4/TiO2 NT photoelectrodes also present excellent photocatalytic and photoelectrocatalytic capabilities in the degradation of methylene blue (MB). The kinetic rate of P-C3N4/TiO2 NTs in the photoelectrocatalytic process for MB is 2.7 times that of pristine TiO2 NTs. Furthermore, the prepared sample was used as a photoanode for solar-driven water splitting, giving a H-2 evolution rate of 36.6 mu mol h(-1) cm(-2) at 1.0 V vs. RHE under simulated solar light illumination. This novel structure with a rational design for a visible light response shows potential for metal free materials in photoelectrochemical applications.

Pure Magneli Ti4O7 nanotube arrays (NTA) were successfully fabricated by reducing TiO2 NTA with hydrogen at 850 degrees C for 30 minutes. The microstructure, composition and electrochemical behavior of the prepared Ti4O7 NTA were characterized by means of X-ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy, Cyclic Voltammetry and Electrochemical Impedance Spectroscopy. The as-prepared Ti4O7 NTA had a highly-ordered tubular structure with high crystallinity, large electrochemical window of water electrolysis (2.4 V vs. Ag/AgCl, pH = 6.0) and low interfacial charge transfer resistance when they were employed as anode for electro-oxidation. Phenol was electro-oxidized on Ti4O7 particles and Ti4O7 NTA with the latter giving 20% more Chemical Oxygen Demand (COD) removal. Pure Ti4O7 NTA also displayed larger degradation coefficient as well as higher COD removal and current efficiency than Boron-doped Diamond and other types of Magneli NTAs. Cathodic polarization was found to be an effective way of restoring the electrochemical performance of oxidized Ti4O7 NTA as an anode. (C) 2014 Elsevier Ltd. All rights reserved.